116 CALIFORNIA ACADEMY OF SCIENCES. 



it. " But surely," he says, "the burden of proof here 

 lies on the side of rny critic. If he can show any suffi- 

 cient reason for going much farther than I have ventured 

 to go in out-Darwining Darwin or for holding that 

 natural selection may not merely help in inducing ster- 

 tlity in some cases, but has been the sole cause of it in 

 all cases then I should welcome his proof as showing 

 that the principles of physiological selection ultimately 

 and in all cases rest on those of natural selection. But, 

 clearly, it is for him to prove his positive: not for me to 

 prove what I regard as an almost preposterous neg- 

 ative."* 



Mr. Meldola also noted the difficulty that physiologi- 

 cal selection must always be subservient to natural 

 selection, because if a race developed through isolation 

 did not possess some advantage over the main stock 

 the struggle for existence being most severe among most 

 closely related forms it would not be able to compete 

 with the dominant type of the species. In reply to this 

 Mr. Romanes states that if the character distinguishing 

 the new form be indifferent as regards utility the in- 

 dividuals possessing it will be on an exactly equal foot- 

 ing with those which do not possess it, more especially 

 if as at first, the variation be simply of the reproductive 

 organs. The fact that the individual possessing this 

 variation has reached the breeding age is in itself a 

 guarantee of its fitness to survive, and it was to empha- 

 size this fact that the alternative name of the " segrega- 

 tion of the fit " was proposed. 



Mr. Wallace has however presented a more sweeping 

 and serious line of criticism than any of the preceding, 

 and it is to this that attention must next be directed. 

 His objections were stated in an article entitled " Romanes 

 versus Darwin. An Episode in the History of the 



*1. c. p. 408. 



